re PR tree-optimization/43833 (false warning: array subscript is above array bounds with -O3)

	PR tree-optimization/43833
	* tree-vrp.c (range_int_cst_p): New.
	(range_int_cst_singleton_p): New.
	(extract_range_from_binary_expr): Optimize BIT_AND_EXPR case
	when both operands are constants.  Use range_int_cst_p in
	BIT_IOR_EXPR case.

	testsuite/
	PR tree-optimization/43833
	gcc.dg/Warray-bounds-8.c: New test case.

From-SVN: r158727